The grizzly bear (Ursus arctos horribilis) is a subspecies of brown bear (Ursus arctos) that generally lives in the uplands of western North America. This subspecies is thought to descend from Ussuri brown bears which crossed to Alaska from Eastern Russia 100,000 years ago, though they did not move south until 13,000 years ago.
A grizzly searches for food high in the mountains as the last of the winter snow melts.
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Ursos arctos horribilis
Grizzlies are normally solitary active animals, but in coastal areas the grizzly congregates alongside streams, lakes, rivers, and ponds during the salmon spawn. Every other year, females (sows) produce one to four young (commonly two) which are small and weigh only about one pound. A sow is protective of her offspring and will attack if she thinks she or her cubs are threatened.
Brown bears are found in Asia, Europe and North America, giving them one of the widest ranges of bear species. The ancestors of the grizzly bear originated in Eurasia and traveled to North America approximately 50,000 years ago. This is a very recent event in evolutionary time, causing the North American grizzly bear to be very similar to the brown bears inhabiting Europe and Asia. In North America, grizzly bears previously ranged from Alaska to Mexico and as far east as the Hudson Bay area. In North America, the species is now found only in Alaska, south through much of western Canada, and into portions of the northwestern United States including Idaho, Montana, Washington and Wyoming, extending as far south as Yellowstone and Grand Teton National Parks, but is most commonly found in Canada. There may still be a small population in Colorado in the southern San Juan Mountains. In September 2007 a hunter produced evidence of grizzly bear rehabilitation in the Selway-Bitterroot ecosystem, in Idaho and western Montana, by killing a male grizzly bear. Its original range also included much of the Great Plains and the southwestern states, but it has been extirpated in most of those areas.
In Canada there are approximately 25,000 grizzly bears occupying British Columbia, Alberta, the Yukon, the Northwest Territories, Nunavut and the northern part of Manitoba. Combining Canada and the United States, grizzly bears inhabit approximately half the area of their historical range. In British Columbia, grizzly bears inhabit approximately 90% of their original territory.
The grizzly bear currently has legal protection in Mexico, European countries, some areas of Canada and in the United States. However, it is expected that the re-population of its former range will be a slow process, due equally to the ramifications of reintroducing such a large animal to areas which are prized for agriculture and livestock and also to the bear’s slow reproductive habits (bears invest a good deal of time in raising young). There are currently about 55,000 wild grizzly bears located throughout North America.
Although grizzlies are of the order Carnivora and have the digestive system of carnivores, they are actually omnivores, since their diet consists of both plants and animals. They have been known to prey on large mammals, when available, such as moose, deer, sheep, elk, bison, caribou and even black bears. Grizzly bears feed on fish such as salmon, trout, and bass, and those with access to a more protein-enriched diet in coastal areas potentially grow larger than interior individuals. Grizzly bears also readily scavenge food, on carrion left behind by other animals
The grizzly bears that reside in the American Rocky Mountains are not as large as Canadian or Alaskan grizzlies. This is due, in part, to the richness of their diet, which in Yellowstone consists mostly of whitebark pine nuts, as well as roots, tubers, grasses, various rodents, army cutworm moths and scavenged carcasses. None of these, however, match the fat content of the salmon available in Alaska and British Columbia.
Plants make up approximately 80%–90% of a grizzly bears’ diet. Various berries make up a large portion of this. These can include blueberries, blackberries, salmon berries, cranberries, buffalo berries, and huckleberries, depending on the environment. Insects such as ladybugs, ants and bees are also eaten, but only if they are available in large quantities. At low quantities, the energy gained is not worth the foraging energy output. When food is abundant, grizzly bears will feed in groups, foraging together. For example, many grizzly bears will visit meadows right after there has been an avalanche or glacier slide. This is due to an influx of legumes, such as Hedysarum, which the grizzlies consume in massive amounts. When food sources become scarcer, however, they separate once again.
In preparation for winter, bears can gain approximately 400 lb, during a period of hyperphagia, before going into a state of false hibernation. The bear often waits for a substantial snowstorm before it enters its den, such behaviour lessening the chances that predators will be able to locate the den. The dens themselves are typically located at elevations above 6,000 feet on northern-facing slopes. There is some debate amongst professionals as to whether grizzly bears technically hibernate. Much of the debate revolves around body temperature and the ability of the bears to move around during hibernation on occasion. Grizzly bears have the ability to “partially” recycle their body wastes during this period. In some areas where food is plentiful year round, grizzly bears skip hibernation altogether.
The grizzly bear has several relationships with its ecosystem. One such relationship is a mutualistic relationship with fleshy-fruit bearing plants. After the grizzly consumes the fruit, the seeds are dispersed and excreted in a germinable condition. Some studies have shown that germination success is indeed increased as a result of seeds being deposited along with nutrients in feces. This makes the grizzly bear an important seed distributor in their habitat.
While foraging for tree roots, plant bulbs, or ground squirrels, bears stir up the soil. This process not only helps grizzlies access their food, but it also increases species richness in alpine ecosystems. An area that contains both bear digs and undisturbed land has greater plant diversity than an area that contains just undisturbed land. Along with increasing species richness, soil disturbance causes nitrogen to be dug up from lower soil layers, and makes nitrogen more readily available in the environment. An area that has been dug by the grizzly bear has significantly more nitrogen than an undisturbed area.
Nitrogen cycling is not only facilitated by grizzlies digging for food, it is also accomplished via their habit of carrying salmon carcasses into surrounding forests. It has been found that spruce tree foliage within 500 m of the stream where the salmon have been obtained, contains nitrogen originating from salmon the bears have preyed on. These nitrogen influxes to the forest are directly related to the presence of grizzly bears and salmon.
Grizzlies directly regulate prey populations, and also help prevent overgrazing in forests by controlling the populations of other species in the food chain. An experiment in Grand Teton National Park, Wyoming, USA, showed that removal of wolves and grizzly bears caused populations of their herbivorous prey to increase. This in turn changed the structure and density of plants in the area, which decreased the population sizes of migratory birds. This provides evidence that grizzly bears represent a keystone predator, having a major influence on the entire ecosytem they inhabit.
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